The state attorney general's office said Brentwood Police Officer Stephen Arkell died before the conflagration on Monday that destroyed the duplex on a quiet suburban street and claimed the life of the suspected gunman, 47-year-old Michael Nolan. Gunshots through the walls and roof of the house sent neighbors and other officers fleeing for cover.

Arkell's body was found on the first floor while Nolan's was found in the garage area. Nolan's father, 86-year-old Walter Nolan, was treated at a hospital and released.

A second officer, Derek Franek, responded minutes later from the neighboring Fremont Police Department and found Walter Nolan out front. He found Arkell dead on the floor near a bullet-sprayed wall and escaped out the back and into the trees as Nolan opened fire on him; Franek did not return fire.

More testing is being done after an autopsy performed Tuesday on Nolan did not determine how he died.

Arkell, who was married and had two teenage daughters, had worked for the Brentwood Police Department for about 15 years as a part-time officer. He helped coach the girls' lacrosse team at Exeter High School, where both of his daughters play.

Bill and Lisa Dow, who own the Brentwood Country Store a few hundred yards from the Brentwood police headquarters, said they trusted the 48-year-old Arkell to take their problems seriously.

"He would come in off duty and just say 'Hey, everything OK?'" said Bill Dow. "Not a lot of cops would do that. I know he just wanted to serve his community."

Authorities said police had never been called to the house before and that Nolan had no criminal record. People in the neighborhood for residents 55 and older told police the father and son had argued before.

Associate Attorney General Jane Young said investigators don't yet know what kind of gun was used or how the fire and explosion were triggered. The investigation will take several days.

The first call came in Monday at 4:02 p.m. and Arkell was shot eight minutes later, Young said. Neighbors said they heard three quick volleys of gunfire and Young said Arkell clearly wasn't expecting the attack.

Police and neighbors heard sporadic gunfire for more than a half hour before black smoke started billowing from the house around 4:50 p.m.

The house burst into flames and video showed flames eating through the roof. Firefighters were kept away from the scene for their safety and soon a massive explosion blew the front off the house. Within an hour, it was leveled.

Gov. Maggie Hassan directed that flags fly at half-staff.

"Officer Arkell bravely answered the call of duty and made the ultimate sacrifice, a heroic demonstration of his commitment to the safety of his fellow citizens," she said in a statement.

Among those extending their condolences was the police department in Greenland, about 20 miles away, which lost its police chief, Michael Maloney in a hail of gunfire during an April 2012 drug raid.

"Our thoughts and prayers are with our Brothers and Sisters in Brentwood," the department posted on its Facebook page.

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